calculate engine power (using WaterJet)

Discussion in 'Powerboats' started by quyetvtt46, May 20, 2014.

  1. quyetvtt46
    Joined: Dec 2008
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    quyetvtt46 Junior Member

    hi guys!
    i have a engine (257kW, 3300 rpm) and a WaterJet (HJ274). Now, i have to check them whether suitable with high speed vessel or not, but i don't have enough information of WaterJet. How can i do? help me, thanks!
    vessel: L=7,5 m; v = 30 knot
    WaterJet: i see in the catalog: 330kW, 3300 rpm
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Have you tried the Hamilton jet website ?
     
  3. Olav
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    Olav arch. nav.

    quyetvtt46,

    I second Mr Efficiency's advice to check out the Hamilton website or probably better to contact the Hamilton staff directly.

    However, you may want to do a rough resistance estimation using say the Savitsky method and then a (again) rough check if your jet can deliver the required thrust with the available power from your engine. Here the empirical method of Denny and Feller might come handy if no other information about the jet performance is known.
     
  4. Nisham
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    Nisham Junior Member

    Hi guys. Just wanna ask will it be a good idea to install a water jet in a fishing vessel?
     
  5. daiquiri
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    daiquiri Engineering and Design

    Waterjets are indicated for high-speed vessels. They are rather inefficient at displacement speeds, compared to propellers.
    So, if your vessel is a displacement one (as I suspect, but you tell me), and if your goal is to save fuel, then a waterjet will not suit your needs.
    You might check this thread too: http://www.boatdesign.net/forums/jet-drives/jet-vs-prop-better-choice-17003.html
    Cheers

    Edit:
    Sorry, my fault! I didn't see your target speed - 30 kts. That is well inside the waterjet usability range.
     
  6. daiquiri
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    daiquiri Engineering and Design

  7. Mr Efficiency
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    Mr Efficiency Senior Member

    If you are likely to "bottom out" regularly, possibly yes, otherwise probably not. Engines driving jets seem to make a very busy sound, but the scenery does not go past fast enough, in most cases, in my admittedly limited experience ! :)
     
  8. Nisham
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    Nisham Junior Member

    Yeah mine is going to be a displacement hull and saving fuel is a concern. Got the idea well now. Thank you two.

    I want bring some changes to the classic fishing vessel designs. specially the stern. Was thinking of a water jet first then now as I know it's can't be, can i use twin screws? Or what restrictions could stop me from? why all the classic fishing vessels have one propeller and a skeg? if you guys have known any good research made upon the topic of fishing vessels can you please share?

    Thanks
     

  9. quyetvtt46
    Joined: Dec 2008
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    quyetvtt46 Junior Member

    thank guys so much!
    Your documents Which are very useful made me more confident in choosing propulsion system for my boat.
    In my book, there are a method to calculate WaterJet, but I don't understand it deeply. However, I made a spreadsheet, which is attached file, rely on it. I hope that everyone help me find error in my table.
    thanks again!
     

    Attached Files:

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